Many modern television receivers have picture-in-picture (pix-in-pix, or PIP) capability, that is, the capability of receiving video signals from two different sources and for combining them to produce a signal which when displayed results in a first image corresponding to a first program in a main viewing area and a second image corresponding to a second program in a secondary (inset) viewing area of the same display screen. The above-mentioned two video sources may be any of the following: two tuners, two baseband video inputs, or a tuner and a baseband video input.
PIP capability, at the present time, tends to be a "high end" feature (i.e., a feature of the more expensive end of the manufacturers line of television receivers). Such high end receivers may also include other desirable features such as multichannel television sound capability.
The broadcasting of multichannel or stereo sound programs for television in the United States is in accordance with the system adopted by the Broadcast Systems Television Committee (BTSC) of the Electronic Industries Association (EIA). This television multichannel sound system (MTS) provides for the transmission of the sum of the left and right stereo audio information (L+R) in a main audio channel in the spectrum space of the television signal formerly occupied by the monophonic audio signal (mono), and for the transmission of the difference of the left and right stereo audio information (L-R), modulated onto a subcarrier. The television multichannel system also provides for the option of simultaneously transmitting a second audio program (SAP) which typically may be used to carry a second language version of the program being provided in the main (L+R) audio channel.
Thus, although some television broadcasters transmit two distinct audio signals on the same television channel, only one video program is transmitted per standard television channel because of limited channel capacity.